Method of making incandescent cathodes



Dec. 22, 1953 E N 2,663,069

METHOD OF MAKING INCANDESCENT CATHODES Filed July 20, 1951 INVENTOR. GE 012GB AESPEIZSEV'.

BY%%//7/QZ AGENT.

Patented Dec. 22, 1953 METHOD OF MAKING INCANDESCENT CATHODES Hudson, N. Y.

Application July 20, 1951, Serial No. 237,695

9 Claims.

types of cathodes where it is essential to make a tight joint between a porous member of refractory metal and a second member of refractory metal which members form a cavity containing an electron emissive material.

Cathodes described in the above-mentioned patent comprise a structure enclosing a cavity containing a supply of electron emissive material which structure has a porous wall portion of sintered refractory material, such as tungsten,

which forms the emissive part of the cathode.

As the pores of this porous portion must form the largest passageways connecting the cavity to the outside of the cathode and as such pores are of extremely small size, it is essential that a very tight joint be made between the porous por- 5 tion and the remaining part of the cathode structure.

The main object of my invention is to produce a tight joint in such cathode structures.

A further object is to provide a simple and inexpensive method of producing such a joint.

A still further object is to produce a joint which remains tight during the operation of the cathode and may even increase in tightness with increasing operating temperatures.

Another object is to produce a tight joint without deleteriously affecting the electron emissive material present in the cavity.

In accordance with the method of my invention, I form the porous body by pressing into the desired shape a mass of particles of refractory metal, such as tungsten and then heat the soformed body at a temperature which is sufficiently high to give the body good mechanical strength. This body, which will be referred to as the presintered body, will usually be sufficiently accurately dimensioned so as to fit with a snug fit, the body with which the tight joint is to be made. However, in some cases I prefer to machine the surface of the porous body so as to obtain the desired snug fit. For this purpose I may use the method disclosed in U. S. patent application s. N. 234,513, filed June 30, 1951 by Roberto Levi.

The presintered porous body is then slipped over the second body which has a' higher volumetric coefficient of expansion than the refrac-- tory material to form a cathode assembly having a cavity in which the electron emissive material is provided. The cathode assembly is then heated at a temperature higher than the first temperature to produce a shrinking action in the porous body and a tight shrunken joint, because the second body will expand to a greater extent than the refractory material.

The temperatures to be used depend upon several factors including the refractory material used, the size of the particles and the pressures used. In the presintering I use a temperature which gives the body good mechanical strength and at the same time is considerably below that temperature to be used in the second heating operation. The temperature used during the second heating operation should be below that temperature at which the electron-emissive material would be deleteriously affected i. e. below its melting point, and at the same time should be sufficiently above the temperature first used to produce the necessary degree of shrinkage action and thus a tight seal. Care must, of course, be taken that the temperature used during the second operation is not so high as to produce an excessive shrinkage action which might tend to crack the porous body.

'I have found that when using a porous tungsten body which is to be jointed to a molybdenum body good results have been obtained when using a temperature of about 900-l000 C. for the presintering operation and a temperature between about 1300 C. and 1800 C. for the sintering or shrinkage operation. However, as stated, the exact temperatures to be used will vary depending upon several factors and one skilled in this art can readily select the same.

To prevent undesired evaporationof the electron emissive material, I prefer to carry out the heating of the cathode assembly in an inert atmosphere, such as helium or argon, or in a slightly reducing atmosphere, such as nitrogen containing a few percent of hydrogen.

In order that my invention may be clearly understood and readily carried into effect, I shall describe the same in more detail with reference to the accompanying drawing in which:

Figure 1 is a sectional side view on an enlarged scale of a dispenser type cathode of the cylindrical type, and

Figure 2' is a sectionized side view of a dispenser type cathode of the end emissive type.

v The cathode shown in Figure 1, which is particularly useful in magnetrons, comprises a tubular member I of refractory metal, for instance molybdenum, provided with a groove 2 containing a supply of electron emissive material 3, such as barium and strontium carbonates. Fitting upon the member l with a shrunken fit is a porous tubular body of sintered refractory material, such as tungsten. A heating filament 5 is located within the bore of member i.

In accordance with the method of the present invention the body 4 is made by pressing, for instance under a pressure of about 2,000 kgJcmE a mass of finely-divided refractory metal such as tungsten in the desired form and'for --this purpose I make use of tungsten powder having a density of 54 gins/in} and comprising the following fractions in the followi'ng'proportions as determined by the elutriation testf" The presintered body t is then slipped over member 9 with the "electron 'einissive material S'present inthe cavity so asto give the cathode structure shown in Figure l.

The -"assembleol cathode structure is then heated in'a'n inert atmosphere such'as helium or "nitrogento-sinter-body 4 with a minimum amount of reduction of alkaline earth compound and-thereby impart a shrinking-action there to s6 --that-- body 4 embraces member l with "a shrunken fit For this purpose I heat the oathode structure to atemper ature which is'con sid erab ly" above the temperatureus'ed in the presintering for instance about 200 C5 to 400C. higher? On the -other*han'd the temperature mu t be below that value at-which the electron emissive materialwould be deleterious'ly affected. Inf-general, I have'found that'when using tungston -temperatures between about 14:00 C'. and 180i)" Cfaresatisfactory) The-cathodeshown in Figure 2, which is of the end-emittingtype comprises a tubular body 6 provided with a parti ion 'l dividing' the bore thereof'into two partsl l i'tting eve-met d of body twith a s hrunken fitis a'cup shaped' por ous' member 8 of refractory metalfsuchats' tungsten; Member 3 forms the upper portion off'body'fi a cavity inwhich is located'a supply 3 of electron emissiy'e material such as bar iu'rlri and strontium carbonates. -*A---heatingffilament 5 is located in the lower part of the body 5 Thebup-shaped 'bodyll is made in a manner similar to" that disclosed in connection with' bod'y 4. after being ss b d fii ec hqde structure, the'entire assembly is heated i -the manner described in connection Figural.

While I] have describedmy' invention connection with specific examples and certaintemperatures, pressures and particle sizesyI do not desire to be limited thereto as obvious modificaas s will readily present themselves to" one skilled in this arty What I claim is:

l. A' method of manufacturing a cathode of the dispenser type oomprisingthe steps of f orming particles of a refractory metal under -pres sure into a hollow body open atone end thereof, presint'ering the so-formed body at a-temperaturehigh" enough" to impart --sufiicient mechanical strength thereto to make s a 01 body self-supporting, forming a second body of a material having a higher volumetric coefficient of expansion than the refractory metal, said second body having a shape adapted to fit into the open end of said first body and forming an internal cavity therewith for containing a supply of alkaline earth metal compound, inserting said sec ond body into said first bo'dy; and heating said first and secondbodies' to a temperature higher than the temperature at which said first body was presintered to tightly close the internal cavity" by internally expanding the second body to a greater extent than the first body.

2. A method of manufacturing a cathode of the dispenser'type comprising the steps of forming particles of tungsten under pressure into a hollow body' open' at one end thereof, presinterifig-thesO-fo'rmed body at a temperature high enough to impart sufficient mechanical strength thereto to make said body self-supporting, forming a second body of a material having a higher-volumetric coefficient of expansion -than thetungstemsaid second body having a'shape adapted. to'fit into-*the open end"of'saidfi'rst body and forming an internal cavity therewith for containing a supply of alkaline earth metal compound; inserting said'second body into'said first'body, and heating said first'and second bodies to a temperature higher than the tem perature'at which said first body was presintered to tightly close'the internal cavity byinternally expanding the second "body to a greater extent than the first body.

31A method of manufacturing a cathode of the dispenser type comprising the steps offo'rm ing particles of tungsten under pressure'into a hollow body operrat one" end thereof; presinter ing the so-formdbody at a temperaturahigli enough to impart'sufficient mechanicarstrength thereto to make said bodyself-supporting forrm' ing a second body of 'molybdenum,"said second body having a shapeadapted to fit into the open end of said first body and forming an internal cavity therewith for containingasupply of alkaline earth metal compound, inserting said'second body into said'first'body; and heating said first body and second bodies to a temperature" higher than the temperature at which said first body was presintered to tightly close the internal cavity by internally expanding the second body'to a greater extent than the first body.

4. A method of manufacturing a cathode of the dispenser type comprising the steps of 'form ing particles of tungsten under pressure into a i hollow body open at one end thereof, presintering the so-formed body at a temperature high enough to impart sufficient mechanical strength thereto to make said body self-supporting, forming a second body of molybdenum, said second body having a shape adapted to fit into the open end of said first body and forming an internal cavity'therewith for containing a supply of alkaline earthmetal compound, inserting said second body into saidfirst bodyyand heating said first and second "bodies to a temperature'higher than the temperature at which said first body was presintered in an inert atmosphere to tightly'close' the internal cavity by internallyexpanding the second body 'toa greater extent than the'firstbody.-""' "5. 'Amethod of manufacturing a cathode of the dispenser type comprisingthesteps of forming particles of tungsten und'er pressure into a hollow body open at one end thereof presintering'the'so 1000 C. to impart sufiicient mechanical strength thereto to make said body self-supporting, forming a second body of molybdenum, said second body having a shape adapted to fit into the open end of said first body and forming an internal cavity therewith for containing a supply of alkaline earth metal compound, inserting said second body into said first body, and heating said first and second bodies to a temperature of about 1300 to 1800 C. to tightly close the internal cavity by internally expanding the second body to a greater extent than the first body.

6. A method of manufacturing a cathode of the dispenser type comprising the steps of forming particles of tungsten under pressure of about 2000 kg./cm. into a body open at one end thereof, presintering the so-formed body at a temperature of about 900 to 1000 C., forming a second body of molybdenum, said second body having a shape adapted to fit into the open end of said first body and forming an internal cavity therewith for containing a supply of alkaline earth metal compound, inserting said second body into said first body, and heating said first and second bodies to a temperature of about 1300 to 1800 C. to tightly close the internal cavity by internally expanding the second body to a greater extent than the first body.

7. A method of manufacturing a cathode of the dispenser type comprising the steps of forming particles of tungsten into a hollow body open at one end thereof, presintering the so-formed body at a temperature of about 900 to 1000 (3., forming a second body of molybdenum, said second body having a shape adapted to fit into the open end of said first body and forming an internal cavity therewith for containing a supply of alkaline earth metal compound, inserting said second body into said first body, and heating said first and second bodies to a temperature of about 1300 to 1800 C. in an non-oxidizing atmosphere to tightly close the internal cavity by internally expanding the second body to a greater extent than the first body.

8. A method of manufacturing a cathode of the dispenser type comprising the steps of forming particles of tungsten under pressure into a hollow body open at one end thereof, presintering the soformed body at a temperature of about 900 to 1000 C. in a non-oxidizing atmosphere forming a second body of molybdenum, said second body having a shape adapted to fit into the open end of said first body and forming an internal cavity therewith for containing a supply of alkaline earth metal compound, inserting said second body into said first body, and heating said first and second bodies to a temperature of about 1300" to 1800 C. in a non-oxidizing atmosphere to tightly close the internal cavity by internally expanding the second body to a greater extent than the first body.

9. A method of manufacturing a cathode of the dispenser type comprising the steps of forming particles of tungsten under pressure into a hollow body open at one end thereof, presintering the soformed body at a temperature of about 900 to 1000 C. to impart mechanical strength thereto, forming a second body of molybdenum, said second body having a shape adapted to fit into the open end of said first body and forming an internal cavity therewith for containing a supply of alkaline earth metal compound, inserting said second body into said first body, and heating said first and second bodies to a temperature of about 1300" to 1800 C. in hydrogen to tightly close the internal cavity by internally expanding the second body to a greater extent than the first body.

GEORGE A. ESPERSEN.

References Cited in the file of this patent UNITED STATES PATENTS Number 

